This invention relates generally to the preservation of large sections of biological tissues, and more particularly to a method which converts such a section, e.g. cross section of a rabbit, into a plastinated sheet. In a method in accordance with the invention, the tissue water of the large section is replaced by a polymer, thereby preserving the large section of biological tissue permanently.
Large sections of biological tissue, especially sections of whole organs and bodies of animal or human origin are often required for teaching and scientific purposes in the fields of anatomy, pathology, forensic medicine, biology and the like.
Large sections have heretofore been preserved by the following methods:
(1) Gelatine--and Paper method: With gelatine preservation, impregnated sections are glued on plates of acrylic resin (Improved Plastic Embedding of Wet Biological Specimens, by Simmons, E. M. et al. in MEDICAL AND BIOLOGICAL ILLUSTRATIONS, 18, 260-262) or on paper (Rapid Paper Sections of Solid Organs, by Whimster, W. F., in Human Pathology 1, 1, 1970).
(2) Embedment: The sections are embedded in blocks of plastic. To this end, a bottom, a specimen and a top layer must be poured (A Simple Method for Embedding Anatomical Specimens, by Grimsrud, O. K., and Dugstad, G., NEURORADIOLOGY 10 143-145, 1975; Preparation of Plastic Mounted Brain Specimens, by Deonar, V., NEURORADIOLOGY 4, 197-201, 1972).
(3) Polymer impregnation: A method of impregnating large sections with uncured polymers with subsequent curing between separating foils is described in "Impregnation of Soft Biological Specimens with Thermosetting Resins and Elastomers," by v. Hagens, G., THE ANATOMICAL RECORD 194, 247,256, 1979.
These known methods as well as the preserved products attained thereby suffer from serious disadvantages, as will now be explained:
(1) Gelatine--and Paper method: The preserved large section is not resistant to scratches (gelatine surface) or to mechanical stress (paper as supporting medium). Because of the acrylic sheet functioning as a supporting medium, the preserved large section is considerably thicker than the tissue section.
(2) Embedment: Due to the bottom and the top layer of cured resin, the thickness of the resulting block is considerably thicker than the large section itself. Details of the specimen cannot be viewed directly with the aid of a magnifier. Because it is necessary to pour three layers of resin at different times and the surface of the cured block has to be ground and polished, this method is quite time-consuming and costly.
(3) Polymer impregnation: Because of the firmness of the polymer material and the minimal thickness of the resulting sections, this method appears to be quite advanced. However, this technique for preserving a large section lacks uniform thickness and surfaces which are even or polished. Moreover, it is very difficult to remove air bubbles in the vicinity of the tissue section.
It is also known from the literature (POLYMER PROCESSES, Vol. X, by Schildknecht, C. E., Interscience Publishers Inc., New York, p. 35, 1956) that acrylic sheets can be made by casting uncured polymer (catalyzed prepolymer or monomer) in a cell defined by glass plates. The glass plates are separated from each other along their outer edges by an elastomeric material in order to prevent leakage of the uncured polymer. These plates are subjected to a constant pressure which causes the plates to move toward each other in the course of polymer shrinkage during polymerization. The resulting transparent sheets of organic glass exhibit a uniform thickness and surfaces which are even and polished. These sheet properties are also desirable in the context of a plastinated sheet preserving a large section of biological tissue.